5th Infantry Regiment (United States) - Mexican-American War

Mexican-American War

On 1 March 1845, three days before he left office, President John Tyler signed a bill establishing an offer by the United States to annex the Republic of Texas, which had broken away from Mexico in 1836, and make it a state. This set off an immediate diplomatic crisis between the United States and Mexico over the southern boundary of Texas. Mexico claimed that the traditional southern boundary of Texas was the Nueces River; the U.S. and Texas claimed it was the Rio Grande, further south. Incoming President James Knox Polk directed Brigadier General Zachary Taylor to form an "Army of Observation" at Corpus Christi, Texas, ostensibly to protect the disputed zone from Mexican invasion. Five companies of the 5th Infantry under the command of Lieutenant Colonel James S. McIntosh reported to Taylor at Corpus Christi on 11 October 1845, two days before Texas voters accepted the annexation offer.

On 9 March 1846, Taylor's army left Corpus Christi to march to the Rio Grande and assert U.S. sovereignty over the expanded area. They arrived on 28 March across the river from Matamoros and built a fortified camp, Fort Texas, on the site of the modern city of Brownsville, Texas. Taylor also established a supply base 27 miles east at Point Isabel, at the mouth of the river.

The 5th marched with Taylor from Fort Texas to Point Isabel in late April to clear their supply route of Mexican troops. While they were fortifying that base, the Mexican Army of the North laid siege to Fort Texas, beginning a bombardment of the post on 3 May. Taylor's army marched back from Point Isabel and met the enemy on 8 May at Palo Alto, several miles east of the fort. In the resulting battle, the 5th Infantry broke a charge by Mexican lancers trying to break through to Taylor's supply train. Over night, the Mexicans withdrew to a better defensive position at Resaca de la Palma, which Taylor's army assaulted on the morning of the 9th. After stiff initial fighting, U.S. dragoons overran the Mexican artillery. The 5th and 8th Regiments then led a charge that broke the Mexican center and routed their army.

Taylor's troops relieved Fort Texas, crossed the Rio Grande into undisputed Mexican territory and occupied Matamoros, where they spent most of the summer. In late August Taylor moved south toward Monterrey, arriving on 19 September 1846. The 5th Infantry was assigned to the division of Brigadier General William J. Worth. The Battle of Monterrey began on 21 September. David Twiggs' division assaulted the city, soon finding itself in house-to-house fighting, while Worth's division went around the city, cutting off its communications. On the 23rd, the 5th Infantry captured Fort Soldado, completing the isolation of the Mexican forces. Worth's division also fought its way into the city, contributing to the Mexicans' decision to negotiate. They surrendered the city to Taylor in exchange for a two months' truce.

After Monterrey the 5th and the other regular regiments in Taylor's command were replaced by volunteers. They returned to Texas to join Major General Winfield Scott's expedition to Veracruz. The whole regiment was now together, though two companies were detached during the march to Mexico City and spent their time defending supply trains from guerilla attacks. Still in Worth's division, the 5th captured Perote on 22 April 1847.

Reaching the outskirts of Mexico City, the 5th was part of the flanking movement that led to the victory at Contreras on 19 August. The following day, they took the right flank in the assault on the bridgehead at Churubusco. The 5th provided storming parties for the assaults on the Molino del Rey on 8 September and Chapultepec Castle on the 13th; the full regiment followed up in the latter seizure. Later on the 13th, the 5th joined in the seizure of the Garita San Cosme, one of the city gates of Mexico City itself. This led to the city's capitulation on the 14th.